Recently, cutting tools, such as inserts and end mills, using cBN sintered materials in the cutting edge parts are provided as working tools for molds used for manufacturing bodies of cellular phones, smart phones, or the like. The cBN sintered material has hardness second only to diamond; and exhibits high productivity and enhanced service life.
However, the cBN sintered material itself is hard to be machined and expensive. In addition, the shape of the sintered material is limited to a discotic shape, and it is impossible to form a tool shape freely. Therefore, the use application of the cBN sintered material is limited.
On the one hand, with increased usage of difficult-to-cut materials, the use application of the cBN sintered material is increasing recently in spite of the difficulty of machining the tools. As a method to overcome the cost and workability problems, there is a method in which the inexpensive and highly workable cutting tool main body made of WC-based cemented carbide; and the cutting edge part made of a material of cBN sintered material are brazed. By using this method, cutting tools, in which the cutting tool main bodies made of WC-based cemented carbide and the cutting edge parts made of a material of the cBN sintered material are bonded, are provided.
For example, a cutting tool, in which a cBN sintered material is bonded on the cutting tool body made of WC-based cemented carbide through a bonding part, is disclosed in Patent Literature 1 (PTL 1). The bonding part is made of one or two of: 15-65 weight % of Ti and Zr; and Cu. And because of this, the cBN sintered material is bonded to the cutting tool body strongly and highly-stiffly without cracking or the like.
In addition, a cutting tool, in which a cutting edge piece made of a cBN-based sintered material is bonded directly on a cutting edge piece brazing part of a cutting tool main body made of WC-based cemented carbide by using a Ag alloy brazing material, is disclosed in Patent Literature 2 (PTL 2). The Ag alloy brazing material has a composition made of: 20-35 weight % of Cu; 1-5 weight % of Ti; 1-20 weight % of In; and the Ag balance including inevitable impurities. The cutting edge piece disclosed in PTL 2 has an excellent brazing bonding strength.
In addition, a joined body is disclosed in Patent Literature 3 (PTL 3). In the jointed body disclosed in PTL 3, a cBN-based sintered material is bonded on the cutting tool body made of WC-based cemented carbide through a bonding part; and a titanium nitride compound layer with a layer thickness of 10-300 nm is formed on the interface between the cBN-based sintered material and the bonding material. In addition, the thickness of the bonding part on the back surface of the cBN-based sintered material is thinner than that of the bonding part on the bottom surface in the jointed body disclosed in PTL 3. Because of these, the jointed body disclosed in PTL 3 has an excellent brazing bonding strength.